1. Field of the Invention
This invention relates to a light emitting device and a method of fabricating the same.
2. Description of the Related Art
Light emitting device having the light emitting layer portion thereof composed of an (AlxGa1−x)yIn1−yP alloy (where, 0≦x≦1, 0≦y≦1; simply referred to as AlGaInP alloy, or more simply as AlGaInP, hereinafter) can be realized as a high-luminance device, by adopting a double heterostructure in which a thin AlGaInP active layer is sandwiched between an n-type AlGaInP cladding layer and a p-type AlGaInP cladding layer, both having a larger band gap. Current is supplied to the light emitting layer portion through a metal electrode formed on the surface of the device. The metal electrode acts as a light interceptor, so that it is formed, for example, so as to cover only the center portion of a first main surface of the light emitting layer portion, to thereby allow light to be extracted from the peripheral region having no electrode formed thereon.
In this case, smaller area of the metal electrode is advantageous in terms of improving the light extraction efficiency, because it can ensure larger area for the light leakage region formed around the electrode. Conventional efforts have been made on increase in the energy of light extraction by effectively spreading current within the device through consideration on planary shape of the electrode, but increase in the electrode area is inevitable anyhow in this case, having been fallen in a dilemma that a smaller light extraction area results in a limited amount of energy of light extraction. Another problem resides in that the current is less likely to spread in the in-plane direction, because the dopant carrier concentration, and consequently the conductivity, of the cladding layer is suppressed to a slightly lower level in order to optimize emissive recombination of carriers in the active layer. This concentrates the current into the region covered by the electrode, and results in decreasing an amount of the substantial light extraction energy from the light leakage region. There has been adopted a method of forming, between the cladding layer and the electrode, a low-resistivity current spreading layer having a dopant concentration larger than that of the cladding layer. On the other hand, there is also proposed a configuration in which a thick and low-resistivity transparent semiconductor layer is disposed on the back surface side of the device, typically by bonding a semiconductor single crystal substrate, so as to use the layer also as the device substrate (Japanese Laid-Open Patent Publication “Tokkai” No. 2001-68731). In both of these cases, provision of the current spreading layer or the transparent semiconductor layer as a transparent thick-film semiconductor layer thickened to a certain degree or more makes it possible not only to improve the current spreading effect in the device plane, but also to further increase the light extraction efficiency because the extracted light energy from the side face portions of the layer can be increased.
In fabrication of the light emitting device having the transparent thick-film semiconductor layer as described in the above, it is general to adopt a method of preparing a wafer having such transparent thick-film semiconductor layer formed thereon, and dicing the wafer to thereby divide it into the individual device chips. In the process of dicing, the side face portions of each device as cutting surfaces, have a process-damaged layer formed therein, and a large number of crystal defects contained in the process-damaged layer are causative of current leakage and scattering, so that it is a general practice to remove, after the dicing, the process-damaged layer by chemical etching.
The removal of the process-damaged layer by any publicly-known chemical etching, however, cannot always be judged by leakage current, because the light emitting layer portion and the transparent thick-film semiconductor layer differ in the chemical composition from each other, and this has been consequently resulting in only an insufficient improvement in the light extraction efficiency from the side face portions of these layers. A method relying upon an excessively strong chemical etching, in view of raising the etching effect of the side face portions, is not adoptable because it may result in roughening of the main surface of the device or in damage of the metal electrodes already formed thereon, and may degrade performances of the device.
It is therefore a subject of this invention to provide a light emitting device having the transparent thick-film semiconductor layer and capable of distinctively raising the light extraction efficiency from the side face portions of the layer, and a method of fabricating such device.